Permanent marks on some bricks?

[Terry Pinnell]

A year ago I had my drive block-paved. I understand they are 'Marshalls' on hardcore plus 'membrane' plus sand. They replaced mainly the original concrete slabs, and a small stretch of lawn. Here's a photo:

I'm pleased with the job. But after a long enough dry spell early this year I noticed that a score or so of the bricks seemed to have dark patches, as if they were permanently damp. Most of these were near the garage entrance, just in front of the drain, as shown here:

that the marks remained identical, not varying at all. (That photo was taken about 2 months ago, yet that area looked exactly the same yesterday morning.) So I have been assuming that the bricks were flawed.

To cut to the quick, it's taken me until yesterday afternoon to get the paver to replace them with new bricks. ("Next week, I promise...", "Tomorrow...", etc, since April!) He rushed it and missed 3 that needed replacing, but as he left me some spares I replaced those myself afterwards.

However I now see that the sand in this area is very wet. Despite having had a few days without rain. So could it be that that's the main cause, not any significant flaw with these particular bricks? Are there perhaps always some porous areas in these bricks that allow moisture to seep through, and darken the top surface in specific patches like this?

If so, presumably this means rainwater is not draining away sufficiently at this small area? So how should I fix that please? Frankly, I don't want the hassle of getting the paver back yet again, so want to do it myself. Can I just remove a few bricks and puncture the membrane in a couple of spots? Would I need to first remove the wet sand and replace it with dry, or would it eventually dry out anyway? I doubt my skill at getting it level again if I do so!

Any advice would be much appreciated please.

[Andy Burns]

[Terry Pinnell]

Strange, thanks for letting me know Andy. They seemed OK when I checked before posting, but something must have screwed up. Here they are again. I can click these in my message composition window and they both open OK:

[Rod]

Could it be that the drainage channel (visible in the picture) is preventing flow from the paved area?

Not suggesting you actually do this, but if you lifted the grilles and drilled holes sideways towards the paved area, would that allow water from underneath to drain away? Are the drainage channels bedded onto some mortar which makes them an impenetrable barrier? Of course, this would only be likely if you have something like clay below everything.

We certainly have some areas that dry out much more readily than others. But nothing quite as permanent as you describe.

[John Rumm]

area that could be leaking?

Where does that linear drain connect to?

Do you know what type of membrane was used in the construction (and in particular was is something impermeable?)

[Kevin]

it looks from the first photo that these are on the lowest point on the drive, and the drain/membrane is actually preventing the water going any further that's under the bricks

[Terry Pinnell]

Rod, John, Kevin:

Thanks all. I'm not really sure exactly what the arrangement is near the drain, but I'm guessing it looks like this in cross section:

suggestion of Rod's makes sense, especially as there *is* a lot of clay here. I don't see that it could do any harm anyway to drill holes in the drain walls, and hopefully it will allow any excess water to flow into it.

A key question is whether the membrane is waterproof or not (the latter I understand being called a 'permeable membrane'). The quote wasn't explicit on that. But if it was impermeable, wouldn't that mean that *all* the bricks over the sloping drive would be showing the same 'dampness marks'? Not just this tiny proportion near the drain? On the other hand, how can a permeable membrane protect against weeds?

The drain simply drops down at its RH end and runs under the garage to some soakaway point somewhere in the back garden.

The possibility that Rod and Kevin have suggested, that the drain is somehow blocking proper drainage at the bottom of the drive, seems to be a logical one to me. I wonder if drilling a dozen 10 mm holes on that side will solve it? Assuming I *can* get the drill in at that angle, and that there's no significant obstruction, like cement.

[John Rumm]

Probably only those near the bottom of the slope.

The purpose of the membrane is not to stop weeds anyway (a popular misconception). 150mm+ of compacted limestone chippings (aka Type 1 MoT) will stop any weeds. The membrane is designed to stop the sub base from migrating into the sub soil.

The drain simply drops down at its RH end and runs under the garage to

A point worth checking is does the soakaway actually work? i.e. if you stick water in the channel, does it empty easily?

If the channel empties easily, then it may indeed be the channel (or its bases - they are usually bedded onto a coarse concrete mix) that is blocking the exit of water from the bedding layer of the blocks.

See the pavingexpert site linked to above for chapter and verse on everything to do with block paving .

[Terry Pinnell]

stop weeds" in his quote and I had indeed been labouring under that misconception!

Yes, it's working OK.

That sounds like an accurate diagnosis to me, thank you. It poses the issue of what to do about it, of course! I was thinking of simply lifting the damp bricks and hammering a long screwdriver or something down to make holes in the membrane and also open up the hard-core a bit. But we have a lot of clay here, so I'm not sure how effective that would be. Hence the idea of trying to get the excess into the shallow drain by drilling holes in the side. Although if there's a lot of surrounding cement that might be difficult. And anyway the water is presumably lying well below the level of such holes, which at most would be about 3-5 cm below the top surface.

BTW, here's another photo (cropped from an original), apparently showing the membrane between the sand and the hard-core.

See the pavingexpert site linked to above for chapter and verse on

Excellent site!

[John Rumm]

How about lifting one or two of the soaked blocks, and then excavating the sand under it down to the Type 1 base. Then have a look and see if water pools there (stick a board over it to stop rain falling directly into the hole!)

If water is pooling in the space were the sand is, then you can see at what level you would need to arrange a drain.

Completely the wrong thing to use. I would guess that your bedding layer is totally full of water at the bottom of the slope.

You may find that puncturing the sheet allows enough to flow out of the sodden area, but then again it might not. No harm in trying though.

(I also note that the edging course of charcoal blocks have not beed bedded onto a concrete haunch and are just sat on sand. That means there is no proper restraint at the edge and the whole edge could fall away. Again have a look at the pavingexpert site for details of how the edge should be done)